Wideband Modeling of CMOS Schottky Barrier Diode Detectors for THz Radiometry

A complete system modeling and characterization of a wideband differential terahertz (THz) direct detector, integrated in a commercial CMOS technology, is presented. The detector consists of a recently developed double leaky-slot lens antenna that operates from 200 to 600 GHz in combination with a differential Schottky barrier diode (SBD) direct detection circuit. The proposed methodology, starting from low-frequency measurements on a standalone SBD, is able to adequately model the spectral radiometric performance. The system noise-equivalent power (NEP) is characterized from 325 to 500 GHz in excellent agreement with the proposed system model. The measured NEP, 20 pW/√Hz minimum and 90 pW/√Hz frequency averaged, is compromised with respect to the average NEP of 2.7 pW/√Hz that was initially predicted by simulations using the process design kit (PDK) model, since the available SBDs are operating beyond their cutoff frequency. The diodes and models provided by the PDK proved to be inaccurate in predicting circuit behavior at these high frequencies. By using the proposed analysis and modeling approaches, an accurate wideband antenna-detector codesign could be applied for future passive THz imaging applications based on CMOS technologies.